Generally, a socket for integrated circuits (hereinafter, referred to as an “IC”) is loaded into a test board or a burn-in board. The socket is connected to measuring devices for measuring the properties of a burn-in chamber, peripheral devices and an IC, thus being used in a system for testing the IC. In this case, the burn-in chamber is used to input and output power and electric signals, which are required to drive the IC, through I/O terminals (input and output terminals) formed on the board.
Among the ICs that have been widely used, a BGA (Ball Grid Array) type of IC is shaped as shown in FIGS. 1 and 2.
The BGA-type IC is defined as an IC which uniformly arranges conductive terminals, that is, balls, throughout the bottom (lower surface) of the IC at regular intervals, thus remarkably reducing the size and thickness of the IC.
Generally, the pitch between the balls formed on the bottom of the BGA-type IC is 0.5 mm, 0.75 mm, 0.8 mm, 1.0 mm, 1.27 mm, 1.6 mm, etc. Each ball has a diameter from 0.3 mm to 0.9 mm.
Further, the height from the lower surface of the BGA-type IC to each ball is set from 0.2 mm to 0.6 mm. As the pitch between the balls is reduced, the diameter and height of the balls are reduced.
Hereinafter, the conventional socket (hereinafter, referred to as a “BGA-type socket”) for loading the above-mentioned BGA-type IC will be examined in detail with reference to FIGS. 2 to 5. The problems with the conventional BGA-type socket will be described in detail.
FIG. 3 is a plan view of the conventional BGA-type socket, FIG. 4 is a vertical sectional view taken along line X1-X1 of the conventional BGA-type socket, FIG. 5 is a detailed view of part of FIG. 4, FIG. 6 is a schematic operational view of the conventional BGA-type socket, and FIG. 7 is a view illustrating the incompletely formed state of a slide, which is an important part of the conventional socket.
The conventional representative socket for loading a BGA-type IC is characterized in that it is provided with pinch-type contacts.
As shown in FIGS. 5 to 7, the conventional BGA-type socket includes contacts 16, a socket body 17, a stopper 18, a lead guide 19, a slide, holder springs 13, and a cover 11. Each of the contacts 16 includes two terminals, that is, a fixed terminal 20 and a movable terminal 21, which contact a corresponding ball of the BGA-type IC. Each contact also includes a contact body and a lead which may be soldered to a PCB. The socket body 17 accommodates the contact body. The stopper 18 and the lead guide 19 which guide the lead are provided under the socket body, and the slide 15 and the cover 11 are provided above the socket body. The stopper 18 supports each contact 16 assembled with the socket body 17. The lead guide 19 functions to guide the position of the lead of each contact 16. The slide includes slide elements 22. When the cover is pressed down by slide cams of the cover 11, the slide moves rightwards, so that each slide element 22 pushes the movable terminal 21 of the corresponding contact 16. Thereby, the movable terminal 21 is spaced further apart from the fixed terminal 20 of each contact, in comparison with the initial distance. The slide rotatably holds IC holders 14, with an IC guide 12 being assembled with the slide. The IC holders 14 are rotatably assembled with the slide to hold the IC. The holder springs 13 elastically support a plurality of IC holders 14. The IC guide 12 functions to guide the position of the IC, when the IC is loaded into the socket. Further, the cover 11 is elastically supported by springs 9 and is constructed to move downwards a predetermined distance. When the cover 11 moves downwards, the slide is moved rightwards by the slide cams, thus opening the contacts.
As shown in FIG. 5, the fixed terminal 20 and the movable terminal 21 of each contact 16 are respectively located to the left and right of the corresponding slide element 22. The fixed terminal 20 and the movable terminal 21 of neighboring contacts are respectively located to the left and right of neighboring slide elements.
That is, the conventional BGA-type socket having the pinch-type contacts constructed as described above is characterized in that one fixed terminal and one movable terminal are provided between neighboring slide elements 22.
The schematic operation of the conventional BGA-type socket having the pinch-type contacts constructed as described above will be described below.
As shown in FIG. 6, the first step represents an initial state. In this case, the cover 11 is located at an upper position by a predetermined elastic force of the cover springs that elastically support the cover 11, and the fixed terminal 20 and the movable terminal 21 of each contact are in close contact with both sides of the corresponding slide element 22.
At the second step, the cover 11 is pressed down by an operating distance S, so that the slide is moved rightwards by the cams provided on the cover. At this time, the right surface of the slide element 22 pushes the movable terminal 21 rightwards, thus opening the corresponding contact.
That is, the fixed terminal 20 is spaced apart from the movable terminal 21 by a predetermined width.
In such a state, the IC is positioned inside the IC guide. Thus, each ball of the IC is located between the fixed terminal and the movable terminal of the corresponding contact.
Finally, at the third step, the cover 11 returns to its original position. At this time, as the slide returns to its original position, each movable terminal 21 also returns to its original position. Thereby, each IC ball contacts the movable terminal 21 and the fixed terminal 20.
The conventional BGA-type socket constructed as described above has the following problems.
First, since the fixed terminal and the movable terminal of the contacts simultaneously enter between neighboring slide elements 22, the two terminals (fixed terminal and movable terminal) require a predetermined moving space. Thus, the space for each slide element 22 is somewhat reduced.
This causes a problem when the slide is manufactured through an injection molding process. That is, as shown in FIG. 7, an incompletely formed state occurs in the central portion of a slide part 30.
In a detailed description, the space for each slide element is relatively smaller than the moving space for two terminals (fixed terminal and movable terminal) of each contact, so that the flow of injected resin for the injection molding process is poor.
Especially when the socket has a very narrow pitch of 0.65 mm or less and the number of balls in a ball grid is 20×20 or more, the above-mentioned problems, such as the incompletely formed state, occur frequently.
Meanwhile, when the number of balls is 30×30 or more, a satisfactory forming process is not realized using current injection forming technology.
Second, the cover of the socket is pressed down, so that the slide is moved rightwards by the cams of the cover, and the movable terminal of each contact is pushed by the corresponding slide element. In this case, the force pushing one movable terminal is usually about 50 (gf). Assuming that the total number of contacts loaded into the socket is 400 (20×20), the slide is pushed with a calculated force of 20 (kgf).
Therefore, by pressing down the cover, a force of 20 (kgf) is applied to the cams of the cover. In proportion to the force, a force of pressing the cover is considerably increased, so that it is difficult for a user to operate the socket.
Supposing that the total number of contacts on the socket is 900 (30×30), a force of 45 (kgf) is required to move the slide. It is difficult to realize such a socket using current socket manufacturing technology and injection molding technology.
Third, the pinch-type contact is provided with two terminals (fixed terminal and movable terminal), so that a lot of material is required to form the contact. Thereby, manufacturing costs are increased.
Fourth, in order to load the IC on the pinch-type contacts, each movable terminal is pushed a predetermined distance by the slide element, so that the movable terminal is elastically deformed. Thereby, the contact is opened. Such a construction is problematic in that the life span of the socket is reduced due to the stress acting on the movable terminal.
Fifth, a different IC guide must be developed according to the size of an IC loaded into the socket. Thus, a different mold for the IC guide must be manufactured, which is inefficient and increases the cost of a product.